Device and method for micro sorbent extraction and desorption

ABSTRACT

This invention relates to a micro cartridge and to a method of using the micro cartridge to sample and extract components of interest from a gas or a liquid. The cartridge contains a sorbent and has passages through which a pressure drop can be created to permit access between the gas or liquid and the sorbent. The micro cartridge is elongated and has one pointed end to fit into the injection port of a suitable analysis instrument where the components of interest are desorbed. The cartridge has two ends that are covered by removable closures and preferably has a diameter of less than 1 millimeter. The cartridge can be used with micro machine components and components made using nano technology.

RELATED APPLICATIONS

The present application is a continuation of non-provisional applicationSer. No. 10/496,516 which is a national phase entry of PCT/CA02/001811,filed Nov. 26, 2002, which claims priority to provisional applicationSer. No. 60/333,062, filed Nov. 26, 2001.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a device for sampling and extractingcomponents of interest from fluid containing particulates into a methodof operation thereof. More particularly, this invention relates to amicro cartridge containing a sorbent where outside access to the sorbentcan be open or closed and the micro cartridge is sized and shaped to fitinto an injection port of a suitable analysis instrument.

2. Description of the Prior Art

It is known to have a needle trap whereby a particulate matter can becollected and directly desorbed into an analytical instrument asdescribed in U.S. patent application Ser. No. 09/771,666. The needle hastwo ends with an extraction trap located between the ends. Both ends ofthe needle are open and the needle is connected to syringe having abarrel and plunger. The barrel and plunger are used to cause air to flowthrough the trap by operating the plunger. An inexpensive hypodermicneedle and syringe can be used to construct and operate the needle trapdevice.

While the needle trap works generally well, the packing or sorbentforming the trap sometimes protrudes or slips completely out of the endof the needle. Also, while the needle trap is portable, it is difficultto use in the field where the analytical instrument is some distanceaway from the location where the sample is taken. The needle isrelatively difficult to make completely airtight after a sample has beencollected and therefore cannot be easily protected from contaminationafter a sample has been taken and before the sample is desorbed into ananalytical instrument. Since packing the needle is a time consumingprocess, the needle trap cannot reasonably be considered to be adisposable item. Also, as with any needle, it must be handled extremelycarefully by a user and is not particularly suited to passive collectionof samples. Further, the needle is relatively bulky. Still further,sometimes, the packing in the needle at an end away from the barrel andplunger will tend to clog with sample matrix, thereby interfering withthe flow of sample and therefore making the sampling and extractionprocess inaccurate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a micro cartridgethat can be made of stainless steel, fused silica or other suitablematerial, the cartridge having two closed ends and containing a sorbent.It is a further object of the present invention to provide a device thatcan be used for sampling and extracting components of interest in asafe, inexpensive and accurate manner whether the device is used foractive sampling or passive sampling. It is a further object of thepresent invention to provide a device that can be used for sampling andextracting components of interest and where the device can be inserteddirectly into an injection port of an analysis instrument. It is afurther object of the present invention to provide a micro device thatcan be used for sampling and extracting components of interests formsmall and living objects. It is a further object of the presentinvention to provide a micro device that can be inserted directly into amicromachined analysis instrument.

It is a further object of the present invention to provide a microcartridge that can be used for sampling and extraction where the devicecan be contained in an airtight housing for transport purposes.

A device for sampling and extracting components of interest from fluidhas an elongated micro cartridge. The cartridge contains a sorbent andhas passages therein through which a pressure drop can be created withinthe cartridge to permit access between the fluid and the sorbent. Themicro cartridge is sized and shaped to fit into an injection port of asuitable analysis instrument where the components of interest can bedesorbed.

A method of using a device for sampling and extracting components ofinterest from fluid, the device having an elongated micro cartridgecontaining a sorbent and having passages therein through which apressure drop can be created within the cartridge to permit accessbetween the fluid and the sorbent. The method comprises exposing themicro cartridge and sorbent to a fluid, inserting the cartridge into aninjection port of a suitable analysis instrument and desorbing thecomponents of interest from said cartridge.

Preferably, after use, the cartridge is disposed of.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a micro cartridge containing asegmented sorbent;

FIG. 2 is a schematic side view of the micro cartridge being enclosed ina sealed housing having two parts;

FIG. 3 is a schematic side view of a micro cartridge where part of thehousing has been removed;

FIG. 4 is a schematic side view of a cartridge located within a housingwherein the housing has an opening that can be closed off;

FIG. 5 is a top view of a carousel for an auto sampler where thecarousel contains receptacles for cartridges;

FIG. 6 is a schematic side view of one receptacle containing microcartridge in part of a carousel;

FIG. 7 is a schematic side view of the micro cartridge affixed to abarrel and plunger;

FIG. 8 is a partial schematic side view of a micro cartridge containinga segmented sorbent;

FIG. 9 is a side view of the micro cartridge device in the injector portof a gas chromatograph where carrier gas is diverted through the deviceduring desorption using a valve;

FIG. 10 is a side view of a liner that is used to divert the flow of gasduring introduction of the micro cartridge;

FIG. 11 is a schematic side view of the micro cartridge located withinan injection port;

FIG. 12 is a graph of exhaustive extraction using micro cartridge;

FIG. 13 is a graph of equilibrium extraction using micro cartridge;

FIG. 14 is a schematic side view of part of a needle used for passivesampling;

FIG. 15 is a schematic view of a passive sampler;

FIG. 16 is a graph of passive sampling results;

FIG. 17 is a graph of the adsorption rate for n-hexane under varying airflow conditions.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the drawings, in FIG. 1, there is shown a micro cartridge 2 having atubular member 4 with two ends 6, 8. The ends 6, 8 are closed withremovable closures 10, 12 respectively. The closure 10 convergesoutwardly and has a centrally located first passage 14 therein. Theclosure 12 has a generally rectangular cross sectional shape and islocated in the end 8. The cartridge 2 is filled with a sorbent 16 havingthree different segments 18, 20, 22. A second passage 24 and a thirdpassage 26 is located in the tubular member 4 at the end 8. The microcartridge 2 is preferably made from metal, glass or other suitably inertmaterial. Preferably, the metal is stainless steel or more preferably,silco steel. The micro cartridge can also be manufactured fromdeactivated metal and fused silica. The micro cartridge can bemanufactured using micromachined technology and/or nano technologymaterials and components. The sorbent materials can be in form of smallparticles larger then the passage 14 to prevent loss of sorbent andcontamination of sample or analytical instrument. The sorbent can alsobe produced by direct in-cartridge in-situ polymerization, for examplethrough the sol-gel process of appropriate monomers liketetramethoxysilane [M. Motokawa, at al. J. Chromatogr. A, 961, 53-63(2002)]. This process results in a highly porous monolithic sorbentinside the cartridge facilitating low resistance to flow of the samplematrix during extraction and carrier fluid during desorption intoanalytical. Since it is a monolith it will more likely remain in thecartridge. To prevent loss of sorbent, the sorbent can be bound to thesurface of the cartridge by using appropriate polymerization processwhich can be obtained in-situ polymerization. The sorbent can containderivatization reagent to react with analytes. The reagent can performvarious functions, including converting unstable analytes to more stableanalogs, enhancement of extraction and detection. For example, whenanalyzing for unstable formaldehyde, pentaflorohydrozamine can be usedto obtain appropriate stable oxime. The formaldehyde is then quantifiedas oxime [J. Koziel, J. Noah and J. Pawliszyn Environmental Science &Technology 35, 1481-1486 (2001)]. The derivatization can also beperformed following the extraction by introducing appropriate reagent tothe micro cartridge after the extraction has been completed.

In FIG. 2, the micro cartridge 2 is located within a sealed housing 28having two removable parts 30, 32. The housing 28 closes off all of thepassages 24, 26 and 14. The same reference numerals are used in FIGS. 2,3 and 4 for the cartridge 2 as those used in FIG. 1 for those componentsthat are identical.

In FIG. 3, there is shown a sectional side view of the cartridge 2 shownin FIG. 2, the cartridge being located in the part 32 of the housing 28.The other part 30 of the housing has been removed and is not shown inFIG. 3. The part 32 closes off the second passage 24 and the thirdpassage 26. The embodiment shown in FIG. 3 with the part 32 of thehousing 28 removed can be used for passive sampling.

In FIG. 4, there is shown a sectional side view of a further embodimentof the invention in which the cartridge 2 is located within a housing38. The housing 38 has an opening 40 therein to connect with passage 14.The housing 38 has a clip 44 thereon so that the housing 38 includingthe cartridge 2 can be clipped on to a particular location or clipped onto a pocket of a user for passive sampling. When the sampling iscompleted, the opening 40 can be plugged with plugs (not shown). Thehousing 38 could have more than one opening 40 corresponding to otherpassages of the micro cartridge 2.

In FIG. 5, there is shown a top view of a carousel 50 as an example ofmulti cartridge holder having a plurality of receptors 52 for receivingmicro cartridges (not shown).

In FIG. 6, there is shown a partial sectional side view of one receptor52 in the carousel 50 with a cartridge 2 inserted therein. It can beseen that the passages 24, 26 and 14 of the cartridge 2 are sealed offwhen the cartridge is located in the receptor.

FIGS. 7 and 8 illustrate the operation of the micro cartridge 2 with asyringe 60. By withdrawing the plunger 62 during sampling andextraction, a well-defined volume of the sample can be drawn through thecartridge by the plunger 62. FIG. 8 illustrates the modified embodimentof the invention where the closure 12 is a thick-walled tubing andopenings 24 and 26 are not used. The sample fluid is drawn through theopening in tubing-closure 12. When the plunger 62 is being pushed induring the desorption step the desorption fluid contained in a syringebarrel 68 is delivered to the sorbent 16 through the opening 64 inclosure 12 and transports desorbed analytes into the analyticalinstrument. There is shown in FIG. 8 a partial schematic side view of amicro cartridge 2 containing a segmented sorbent with segments 18, 20,22 mounted into a syringe via closure 12 with a help of a nut 74 and aferrule 78. Syringe contains the threaded receptacle 72 for the nut 74.Using similar connections, the micro cartridge can be connected to pumpor other device which can draw or pump sample fluid. The embodiment ofinvention showed on FIG. 1 can also be operated during sampling in asimilar way by sealing the ferrule around tubing 4 rather then closure12. In such arrangement, the fluid would be drawn via opening 24 and 26.

Use of such micro cartridges in combination with a syringe allows forconvenient sampling. The micro cartridge can be a needle, but ispreferably not a micro cartridge. The device can be used as activesampler, by drawing the gas or liquid sample through the microcartridge, for example, when using a gas tight syringe attached to themicro cartridge (FIG. 7). As FIG. 8 indicates, the preferred sorbentarrangement in the micro cartridge consists of several layers orsegments 18, 20, 22 of sorbent. Weak sorbent 18 (for example:Poly(dimethylsiloxane) PDMS) is located closest to the cartridgeopening, followed by medium strength sorbent 20 (for example:Polydivinylbezene polymer DVB) and strongly binding sorbent 22 such asactivated carbon. This arrangement of sorbent facilitates efficientdesorption since easily extracted components are trapped by the weaklybinding sorbent 18, which is located closest to the exit. The flow ofthe desorption fluid is reversed in the desorption step compared to flowof the matrix in the extraction step and therefore this arrangementfacilitates quantitative desorption. Active sampling can be performed,either in exhaustive mode by trapping all analytes present in therelatively small volume of a drawn air (FIG. 12 and Table 1), or, inmicroextaction mode when equilibrium is reached between air and thesorbing material after a substantially larger sample volume passesthrough the micro cartridge (FIG. 13 and Table 2). In exhaustiveextraction, cooling of the micro cartridge would be beneficial since itallows quantitative trapping for larger volumes of samples.

TABLE 1 Exhaustive extraction with Micro Cartridge Device (MCD) Mass(ng) extracted 2 ml of sample item Octane Nonane Decane Undecane Blank0.00 0.00 0.00 0.00 Carry-over 0.00 0.00 0.00 0.00 Needle desorption0.31 1.22 0.97 1.34

TABLE 2 Equilibrium microextraction with Micro Cartridge Device (MCD)Mass (ng) extracted 32 ml sample item Octane Nonane Decane UndecaneExpri. 1 0.98 2.33 2.62 7.12 Expri. 2 0.68 2.48 2.89 7.24 Expri. 3 0.712.33 2.90 7.22

The major disadvantages of using the syringe during desorption includeintroduction of the oxygen to the sorbent and insufficient amount ofdesorption gas to quantitatively move all analytes from the sorbent tothe analytical device. In FIG. 9, there is shown a schematic side viewof a preferred desorption process in which the trapped compounds aredesorbed thermally into the gas chromatograph 80 using a carrier gasdiverted to the micro cartridge with a help of a valve 82. Flowcontroller 90 supplies a well defined flowrate of a carrier gas to valve82 via tubing 94 which in turn delivers the carrier gas either to theinjection port 96 via tubing 92 or to micro cartridge 2 via tubing 86.The micro cartridge 2 is connected to the tubing 86 containingreceptacle 88 in a similar way to syringe shown in FIG. 8 with a help ofnut 74 and ferrule 78. After the micro cartridge is placed in the linerof the injection port 96 of the gas chomatograph 92, the gas isdiverting from flowing directly to the injector via tubing 92 to flowingthrough tubing 86 and micro cartridge to the liner located in theinjection port. The carrier gas removes the analytes from the sorbentinto the gas chromatograph. The thermal desorption can be simplified ifthe structure of the sorbent in the micro cartridge consists of layersof different sorbing characteristics divided into segments (as shown inFIG. 1) by locating the weakest sorbent close to the entrance passage 14and the strongest sorbent deepest into the cartridge 2 near the closure12. In this arrangement, the middle sorbent is preferably of mediumeffectiveness. This will result in the analytes that are the mostdifficult to adsorb, being adsorbed on the third sorbent from theentrance, the analytes of medium difficulty will be adsorbed on thesecond sorbent from the entrance and the easiest analytes to adsorb willbe adsorbed on the first sorbent from the entrance. The analytes arethen adsorbed throughout the three segments. If the strongest adsorbingsorbent is located nearest the entrance or if only one strong sorbent isused, the sorbent will adsorb strongly binding analytes so well that itwould be difficult to desorb analytes from the cartridge.

FIG. 10 illustrates the preferred desorption approach, which does notrequire a valve, but rather uses a liner 46 containing a restriction 48to divert the carrier gas flow through the cartridge, when the microcartridge 2 is introduced through the septa (not shown) into the liner.There is shown a schematic side view of the cartridge 2 located in theliner 46. The restriction of the liner seals the cartridge 2, whichfacilitates the diversion of flow of gas through the sorbent 16 byclosure of the gas path to a column 36 during the introduction of thecartridge 2 into the injection port. The carrier gas is forced to enterthe micro cartridge through the openings 24 and 26 pass through thesorbent 16 and effectively transfers the analytes into column 36 whichis also sealed by the restriction producing very low dead volume. Thecarrier gas flow direction is indicated by broken arrows. Analytetransfer to analytical instruments for separation and quantification canbe also facilitated with liquid desorption (using solvents or water).Liquid desorption can be accelerated by using a high temperature. Thesystem can be designed to perform sampling and desorption directly inthe field using on-site instrumentation.

As FIG. 11 illustrates, a further embodiment of micro cartridge 2 has atapered tubular member 4, which would also facilitate sealing in theliner 46 with restriction 48. This embodiment does not contain theclosure 10, but rather the tubular member 4 has a domed end with a smallopening 14 in the center. Alternatively micro cartridge 2 could havetiny side openings (not shown) in place of the center opening 14 or itcould have tiny openings in the cartridge tip or free end if sorbent isbonded to the inner surface of the tubular member 4 of a micro cartridge2 (also not shown). The tiny openings must be much smaller compared tothe inside diameter of the needle to prevent the loss of sorbent.

The needle trap can also be used as passive sampler when the needle isexposed to the sample directly allowing components of the sample todiffuse into the needle (FIGS. 14, 15 and Table 3). To extend theintegration time, the diffusion path can be made longer by placing themicro cartridge inside a holder, which has small opening 40 asillustrated on FIG. 4. This results in independence of the sampling ratefrom the sample matrix convection conditions (see FIG. 17). The adsorbedcompounds can be desorbed thermally into the analytical instrument withthe help of flowing gas. The thermal desorption is simplified if thestructure of the sorbent consist of layers of different sorbingcharacteristics, such as the weakest sorbent is close to the exit andthe strongest deepest in the cartridge (see FIG. 1).

TABLE 3 Passive Time Weighted Average Sampling (TWA) with MCD Mass (ng)Extracted Extraction time Octane Nonane Decane Undecane 30 min 0.53 0.700.47 0.67 1 hr 1.05 1.14 0.74 1.13Theory of Passive Time Weighted Average (TWA) Sampling with a MicroCartridge Device (MCD).

FIG. 15 depicts a MCD passive sampler, which consists of a sorbentpositioned a distance L from an opening of fixed cross-sectional area Aopening 14. The important properties of the passive sampler are itsphysical dimensions and the efficiency of the sorbent.

The basic process of analyte uptake by the MCD passive sampler can bedescribed by Fick's first law of diffusion (eq 2)

$\begin{matrix}{J = {- {D( \frac{dc}{dL} )}}} & (2)\end{matrix}$

where D is the analyte diffusion coefficient (cm² min⁻¹), dc/dL is theanalyte concentration gradient from the opening of the sampler to thesurface of the sorbent, and J, which is defined as

$\frac{dn}{Adt},$

describes the flux of the analyte:

$\begin{matrix}{\frac{dn}{Adt} = {{- D}\frac{dc}{dL}}} & (3)\end{matrix}$

where dn is the amount of analyte passing through a cross-sectional areaA during a sampling period dt. dn is proportional to the linearconcentration gradient in the sampler (dc/dL) and the analyte diffusioncoefficient D. For a given sampler, both cross sectional area A anddiffusion path length L are constant. When sampling reaches the steadystate:

$\begin{matrix}{\frac{dc}{dL} = {\frac{\Delta \; C}{L} = \frac{C_{sorbent} - C_{face}}{L}}} & (4)\end{matrix}$

If the sorbent has a large capacity and strong affinity for targetanalytes, i.e. acts as a zero sink, C_(sorbent), the concentration ofanalyte at the sorbent/gas interface, is negligible. In thesecircumstances, eq 4 reduces to:

$\begin{matrix}{\frac{dc}{dL} = \frac{- C_{face}}{L}} & (5)\end{matrix}$

If C_(face) the analyte concentration at the opening, is equal toC_(bulk) (the bulk analyte concentration), which is true when thesampled matrix is well agitated, then:

$\begin{matrix}{\frac{dc}{dL} = \frac{- C_{bulk}}{L}} & (6)\end{matrix}$

substituting eq 6 into eq 3, we obtain, after rearrangement:

$\begin{matrix}{{dn} = {\frac{AD}{L}C_{bulk}{dt}}} & (7)\end{matrix}$

Because the dimensions of the expression

$\frac{AD}{L}$

are cm³ min⁻¹, it is defined as the formal sampling rate S_(R):

$\begin{matrix}{S_{R} = \frac{AD}{L}} & (8)\end{matrix}$

This definition indicates that sampling rate, S_(R), is proportional tothe cross-sectional area, A, and the analyte diffusion coefficient, D,and inversely proportional to the diffusion path length, L. Combing eqs7 and 8 yields eq 9:

dn=S_(R)C_(bulk)dt  (9)

and after integration of both sides over time, eq 9 reduces to:

$\begin{matrix}{n = {S_{R}{\int_{t_{1}}^{t_{2}}{C_{bulk}\ {dt}}}}} & (10)\end{matrix}$

which describes the passive sampler response to a transientconcentration of an analyte as a function of time. For a constantanalyte concentration, eq 10 reduces to:

$\begin{matrix}{n = {S_{R}C_{bulk}t}} & (11) \\{S_{R} = \frac{n}{C_{bulk}t}} & (12)\end{matrix}$

orEquation 11 indicates that the rate of uptake of analyte mass by thepassive sampler (n/t) is directly proportional the sampling rate of thesampler S_(R) and the bulk analyte concentration.

According to eq 8, the sampling rate, S_(R), will be a constant for agiven analyte and passive sampler, and can be determined theoretically.Sometimes, however, it is difficult to determine S_(R) theoretically,especially when the diffusion coefficient is not available. In thesecircumstances eq 12 indicates that an empirical approach can be used—themass loading, n, is determined during a sampling period, t, at aconstant concentration C_(bulk). When S_(R) is determined, it can beused to quantify unknown analyte concentrations by use of eq 13

$\begin{matrix}{C_{bulk} = \frac{n}{S_{R}t}} & (13)\end{matrix}$

It is in this way that the micro cartridge can be used practically as apassive sampler.

Standard Gas Generator

n-Pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane,n-undecane, carbon disulfide, and toluene were purchased fromSigma-Aldrich (Mississauga, ON, USA). ORBO™-32 tubes, gas purifiers,Teflon™ tubing, syringes, Thermogreen septa, gas sampling bulbs, andvials were purchased from Supelco (Mississauga, ON, USA). The timer waspurchased from VWR (Mississauga, ON, USA). Ultra-high-purity hydrogen,nitrogen, and helium were purchased from Praxair (Waterloo, ON, USA).Personal air pumps and the mini-Buck calibrator were purchased from A.P.Buck (Orlando, Fla., USA). Ultra-pure air for the standard gas generatorand for flame ionization detection was supplied by a Whatman zero airgenerator (model 76-803).

National Institute of Standards and Technology (NIST) traceablecertified permeation tubes (Kin-Tech Laboratories, La Marque, Tex., USA)were used for generation n-alkanes. Ultra-high-purity air at 50 psig wassupplied by use of thoroughly cleaned copper tubing and Swagelok™connectors. The supplied air was also scrubbed by use of a Supelpure HChydrocarbon trap before entering the standard gas generator. Allpermeation tubes were placed inside a glass permeation cylinder(KIN-Tech Laboratories, La Marque, Tex., USA) and swept with a constantflow of dilution air. The actual air flow rate was verified by use of aprimary gas flow standard Mimi-Buck calibrator (A.P. Buck, Orlando,Fla., USA). A wide range of concentrations of n-alkanes was obtained byadjusting both air-flow rates and permeation cylinder temperature.

Sampling Chamber

Sampling-chamber temperature was maintained at 25±0.3° C. To investigatethe effect of face velocity, a multi-chamber with three differentdiameters was installed downstream from the main sampling chamber. Thestandard gas generator and sampling chambers were validated by use ofORBO™ adsorbent tubes combined with A.P. Buck I.H. personal air pumpsfor conventional NIOSH methods.

Discussion of the Results.

For the exhaustive extraction (see FIG. 12) the concentration of analyteC can be calculated using the equation 1:

$\begin{matrix}{C = \frac{M}{V}} & (14)\end{matrix}$

where M is the mass extracted and V is volume of the sample. Thereforeusing data from Table 1 we can estimated the concentration of analytesin the standard gas to be about 0.15 ng/ml for Octane, 0.61 ng/ml forNonane, 0.49 ng/ml for Decane and 0.67 ng/ml for Undecane.1. For equilibrium extraction (see FIG. 13) from large sample volume,the mass extracted can be expressed as:

M=KV_(e)C  (15)

where the V_(e) is the volume of the absorbing sorbent (in ourexperiment we used poly(dimethylsiloxane)—PDMS) and K is thesorbent-matrix distribution constant. The data from the Table 2 indicatethat there is an advantage in using equilibrium methods rather thenexhaustive extraction methods since more analytes are extracted forsamples larger then breakthrough volumes. However, the quantitation ismore involved, specially for complex samples since the K needs to beprecisely defined. Using the data from Tables it is possible to find outthat the ratio of K for decane and undecane is about 2, whichcorresponds to literature value (J. Pawliszyn, Solid PhaseMicroextraction, Wiley, NY 1997).2. For time-weighted average sampling (see FIG. 16) the amount ofaccumulated compound on the sorbent as a function of time can beexpressed as:

$\begin{matrix}{M = {\frac{AD}{Z}{\int{C{t}}}}} & (16)\end{matrix}$

where A is the surface area opening of the side-hole and D is thediffusion coefficient of the analyte in the matrix. Table 3 shows thatthe amount of analytes diffused and trapped onto the sorbent isproportional to time as the amount of extracted analytes is doubled byextending exposure from 30 minutes to 1 hour. The above examples clearlydemonstrate that a single micro cartridge can perform all three modes ofextraction.

The important condition for proper operation of the TWA sampler is thatbulk analyte concentration, C_(bulk), must equal the analyteconcentration at the face of the opening, C_(face) i.e.,C_(bulk)=C_(face). A passive sampler can be expected to sampleaccurately if, essentially, all resistance to analyte transport iscontained within the stagnant air layer inside the device. As thevelocity of air across the sampler surface (face velocity) decreasesexternal resistance to mass transfer associated with convectionincreases. When this latter resistance becomes a significant fraction ofthe internal diffusional resistance the mass of analyte collected willbecome less than that predicted on the basis of Fick's first law ofdiffusion. This suggests that a minimum air velocity is required andthat when this minimum is achieved performance will bevelocity-insensitive over a wide range. For a typical passive sampler, alarge surface area is required to ensure a large amount of analyte issampled, to satisfy analytical detection limits. A large surface area,in turn, requires a large face velocity, usually 15 to 50 ft min⁻¹, toensure that C_(bulk) is equal to C_(face).

Micro Cartridge Device (MCD) takes advantage of thermal desorption,which transfers all the collected analytes into the instruments used forquantification, thus enhancing analytical sensitivity. A MCD sampler,for which the cross-sectional area of the opening is very small,requires a very small face velocity only. Experimental assessment ofvelocity-dependence indicated there were no significant effects of usingthe sorbent system with small diffusion orifice at a face velocity aslow as 0.6 cm min⁻¹ (FIG. 17). This is a significant advantage of theMCD device over other passive samplers and means that, in practice, themicro cartridge device can be used for TWA passive sampling withoutconsidering the face velocity problem, which must be taken seriouslywhen deploying other passive samplers.

The components of the sample can be both chemical compounds as well asparticulate matter present in the sample. Fractionation is also possibleduring the desorption in a manner similar to how it is presentlyperformed in solid phase extraction (SPE). Different solvents and/ortemperatures can be used to separate interferences from target analytes.

Preferably, the passages in the cartridge of a size that issubstantially smaller than a cross section of the cartridge. Though notessential, it is also preferable that there are means to cool thecartridge when there is access between the fluid and the sorbent andthere are means to heat the cartridge during desorption. While the microcartridge is described as being used to sample and extract components ofinterest from a fluid, the fluid would most often be air. The sorbentcan consist of small size particulate material or highly porousmonolithic sorbent prepared by polymerization of appropriate monomersdirectly in the micro cartridge. The monolithic sorbent can be derivedfrom a sol-gel process. The sorbent can be bound to the inner surface ofthe micro cartridge. The sorbent can also have a reagent whichselectively reacts with components of interest.

The analysis instrument can be a capillary gas chromatograph where thefluid is a gas or a liquid chromatographic instrument where the fluid isa liquid. A capillary electrophoresis instrument is also suitable. Inaddition, the analysis instrument can be a micro machined instrument.

The passage where the fluid to be sampled enters the micro cartridge isan inlet. Preferably, the micro cartridge has an outside diameter thatis substantially less than two millimeters and, still more preferably,the cartridge has an outside diameter that is substantially less than 1millimeter.

The housing can be completely sealed when it encloses the microcartridge or it can have one or more openings that correspond topassages in the micro cartridge. The openings can have plugs in them toseal the openings.

1. A method of using a device for sampling and extracting components ofinterest from fluid, the device having an elongated micro cartridgecontaining a sorbent and having passages therein, to permit accessbetween said fluid and said sorbent, wherein there is a housing intowhich said micro cartridge can be removably placed, said housing havingan opening therein corresponding to a passage in said cartridge, saidopening having a removable seal and a substantially small diametercompared to a length of said opening, said micro cartridge being sizedand shaped to fit into an injection port of an analysis instrument wherethe components of interest can be desorbed, said method comprisingexposing the micro cartridge and sorbent to a fluid, inserting saidcartridge into an injection port of the suitable analysis instrument anddesorbing the components of interest from said cartridge, said methodfurther including the steps of placing the cartridge in said housing,sealing said housing and sealing said opening with a plug, removing saidplug immediately before sampling, carrying out sampling by diffusionwhile said cartridge is in said housing, replacing said plug in saidopening when sampling has been completed, transporting the housing andcartridge to the analysis instrument, removing the cartridge from thehousing, placing the cartridge into an injection port of the analysisinstrument and carrying out desorption; and wherein the injection porthas a liner and desorption is carried out directly from said cartridgeto said liner, said liner containing a restriction sealing saidcartridge during desorption to prevent desorption fluid from enteringsaid cartridge through the passage used for sampling and permitdesorption fluid to enter said cartridge through another passage in saidcartridge so that desorption fluid flows through the sorbent and thenout through the passage used for sampling.
 2. A method as claimed inclaim 1, wherein said cartridge is connected to the injection port ofthe analytical instrument so that fluid can flow through said cartridgeinto said port to assist in desorption.
 3. A method as claimed in claim1 including the steps of using the cartridge for sampling off site,inserting the cartridge into a sealed housing after completing saidsampling, transporting the housing to the analysis instrument andremoving the cartridge from the housing.
 4. A method as claimed in claim3, wherein said analytical instrument is automated, said methodincluding the steps of automatically removing a micro cartridge fromsaid cartridge holder and placing said micro cartridge into theinjection port of the analytical instrument and automatically carryingout desorption.
 5. A device for sampling or extracting a component ofinterest from a fluid, said device comprising an elongated microcartridge, said cartridge containing a sorbent and having passagestherein to permit access between said fluid and said sorbent, whereinthere is a housing into which said device can be removably placed, saidhousing having an opening corresponding to a passage in said cartridgeto enable sampling by diffusion through said cartridge while saidcartridge remains in said housing, said opening having a removable sealand a diameter substantially small compared to a length of the opening,said micro cartridge being sized and shaped to fit into an injectionport of an analysis instrument where said component of interest can bedesorbed; and wherein the injection port has a liner and desorption iscarried out directly from said cartridge to said liner, said linercontaining a restriction sealing said cartridge during desorption toprevent desorption fluid from entering said cartridge through thepassage used for sampling and permit desorption fluid to enter saidcartridge through another passage in said cartridge so that desorptionfluid flows through the sorbent and then out through the passage usedfor sampling.
 6. The device according to claim 5, wherein said cartridgeis connected to an injection port of the analytical instrument so thatfluid can flow through said cartridge into said port to assist indesorption.
 7. The device according to claim 5, wherein the sorbent hasa reagent that selectively reacts with the components of interest. 8.The device of claim 5, wherein there are means to heat said cartridgeduring desorption.
 9. A device as claimed in claim 5, wherein thecartridge is sized and shaped to fit within a cartridge carousel of saidanalysis instrument, said analysis instrument being automated, saidcarousel having at least one cartridge receptor therein, said passagesbeing sealed when said cartridge is located in the receptor.
 10. Anapparatus comprising a device as claimed in claim 5, wherein theapparatus has a housing into which said device can be inserted andremoved, said housing having an opening corresponding to a passage insaid cartridge to enable sampling through said cartridge while saidcartridge remains within said housing by diffusion, said opening havinga removable seal and a diameter substantially smaller than a length ofthe opening.
 11. An apparatus comprising a device as claimed in claim 5,wherein the sorbent is present across a cross-section of themicrocartridge.
 12. A device as claimed in claim 5, wherein thecartridge is sized and shaped to fit within a cartridge carousel of saidanalysis instrument, said analysis instrument being automated, saidcarousel having at least one cartridge receptor therein, said passagesbeing sealed when said cartridge is located in the receptor.
 13. Adevice as claimed in claim 5, wherein the passages comprise a sidepassage in the side of the cartridge for use during desorption which issealed during sampling to allow sampling from other of said passagesfurther from an inlet end.
 14. A device for sampling or extracting acomponent of interest from a fluid, said device comprising an elongatedmicro cartridge, said cartridge containing a sorbent and having passagestherein to permit access between said fluid and said sorbent, whereinthere is a housing into which said device can be removably placed, saidhousing having an opening corresponding to a passage in said cartridgeto enable sampling through said cartridge while said cartridge remainsin said housing, said opening having a removable seal and a diametersubstantially small compared to a length of the opening, said microcartridge being sized and shaped to fit into an injection port of ananalysis instrument where said component of interest can be desorbed;and wherein the injection port has a liner and desorption is carried outdirectly from said cartridge to said liner, said liner containing arestriction sealing said cartridge during desorption to preventdesorption fluid from entering said cartridge through the passage usedfor sampling and permit desorption fluid to enter said cartridge throughanother passage in said cartridge so that desorption fluid flows throughthe sorbent and then out through the passage used for sampling.
 15. Thedevice according to claim 14, wherein said cartridge is connected to aninjection port of the analytical instrument so that fluid can flowthrough said cartridge into said port to assist in desorption.
 16. Thedevice according to claim 14, wherein the sorbent has a reagent thatselectively reacts with the components of interest.
 17. The device ofclaim 14, wherein there are means to heat said cartridge duringdesorption.
 18. The device of claim 14, wherein the sorbent is presentacross a cross-section of the microcartridge.
 19. An apparatuscomprising a device as claimed in claim 14, wherein the apparatus has ahousing into which said device can be inserted and removed, said housinghaving an opening corresponding to a passage in said cartridge to enablesampling through said cartridge while said cartridge remains within saidhousing by diffusion, said opening having a removable seal and adiameter substantially smaller than a length of the opening.
 20. Adevice as claimed in claim 14, wherein the sorbent is present across across-section of the microcartridge.